Hello and thank you for contacting the Toolset support.
I run a test on a clean install and I was not able to reproduce this issue on a page template. You can log into my test site with this link hidden link
I created a template for the sample page here hidden link
No errors were displayed on the admin, and nothing was written to the debug.log file. Maybe I am missing something. Would you like to try reproducing the issue on my test site? Can you also record a screencast so I can see the same error as you and the steps to follow to trigger it?
If the issue is not reproduced on my test site, we can assume that it is an exception that appears only on your website, we'll need to isolate it from other plugins, and we may also need to check it on a different server to exclude any possible server issues. Let me know if we can take a copy of your website?
I have replicated enough of my environment on your test site to recreate the error. I used query monitor to spot the error and added a single field that needs validation. See the snap. Thanks, James